Effect of divertor geometry on boundary and core plasma performance in ASDEX Upgrade and JET

A key element in future toroidal magnetic fusion machines like ITER is the design of a divertor, which allows for safe particle and power exhaust in p arallel with high bulk plasma performance. Correspondingly. the definition and design of an optimized divertor is a major task within the ongoing inte rnational ITER research and development effort. In order to provide a profo und physics basis for such a divertor optimization, different divertor geom etries are being tested on major tokamaks. This paper describes the effects of these divertor modifications on plasma performance in ASDEX Upgrade and in JET. In conclusion, increasing closure improves divertor performance without limiting the core plasma performance in ELMy H-modes.